Cream butter, shortening, and brown sugar thoroughly. Blend in egg and molasses. Sift together the remaining ingredients. Stir into sugar mixture. Shape dough into 3/4-inch balls. Place 2 inches apart on greased baking sheets. Flatten each ball with the bottom of a glass that has been greased and dipped into sugar. Bake in preheated 350 degrees F. oven for 12 to 15 minutes. Cool cookies on racks and store in airtight tins. Makes 4 dozen cookies.